Number of times engines entered a routine to check for disk I/O. The io polling process count configuration parameter controls the frequency of this check.
When a task needs to perform I/O, the Adaptive Server engine running the task immediately issues an I/O request and puts the task to sleep, waiting for the I/O to complete. The engine may process other tasks, but continues to check for completed I/Os. When the engine finds completed I/Os, it moves the task from the sleep queue to the run queue.
Number of times an I/O was outstanding when the disk check routine was entered.
Adaptive Server engines poll for network I/O when
the value for "io polling process count" tasks
have been run within one tick of the server or during the "idle
loops". However, the engine does not poll for
Disk IO unless there is at least one pending Disk IO. "Checks
Returning IO" indicates the number of times
the engine intends to check for a disk IO and the number of times
Adaptive Server intended to check and there was at least one pending
disk IO.
For example, if an engine checks for expected I/O 100,000 times, this average indicates the percentage of time that there actually was I/O pending. If, of those 100,000 checks, I/O was completed 10,000 times, then 10% of the checks were effective, and the other 90% were overhead.
However, you should also check the average number of I/Os returned per check, and how busy the engines were during the sample interval. If the sample includes idle time, or the I/O traffic is sporadic, it is possible that a high percentage of the checks were returning I/O during the busy period.
If the results in this category seem low or high, you can configure i/o polling process count to increase or decrease the frequency of the checks.
For more information about configuration parameters, see Chapter 5, “Setting Configuration Parameters,” in the System Administration Guide, Volume 1.
Percentage of “Checks Returning I/O” that result in one or more completed I/Os.
Increasing the amount of time that Adaptive Server engines wait between checks may result in better throughput because Adaptive Server engines can spend more time processing if they spend less time checking for I/O. However, you should verify this for your environment. If the value for I/O Busy% is high, then Adaptive Server should perform more frequent checks to pick up I/Os as soon as they are completed. The i/o polling process count configuration parameter controls how often Adaptive Server performs this check.
For more information about configuration parameters, see Chapter 5, “Setting Configuration Parameters,” in the System Administration Guide, Volume 1.
